Device to increase the residence time of liquid in thin film apparatus



Jan. 11, 1966 Filed Jan. 25, 1963 H. U. ELLENBERGER DEVICE TO INGREAS B THE RESIDENCE TIME OF LIQUID IN THIN FILM APPARATUS 2 Sheets-Sheet 1 a l w 1110110111,, 1

INVENTOR #l/YJ' l/lR/Cl/ 54L E/VBE RG51? 4rr0 NEYS Jan. 11, 1966 H. u. ELLENBERGER 3,228,453

DEVICE TO INCREASE THE RESIDENCE TIME OF LIQUID IN THIN FILM APPARATUS Filed Jan. 25, 1963 2 Sheets-Sheet 2 United States Patent 3,228,453 DEVICE T 0 INCREASE THE RESIDENCE TIME (BF LIQUID IN THIN FILM APPARATUS Hans Ulrich Ellenberger, Zurich, Switzerland, assignor to Luwa A.G., Zurich, Switzerland, a corporation of Switzerland Filed .l'an. 25, 1963, Ser. No. 253,872 Claims priority, application Switzerland, Jan. 25, 1962, 916/ 62 4 Claims. (Cl. 1596) The present invention relates to means for increasing the residence time of liquid in thin film apparatus. In thin film evaporators and similar continuously operating heat transfer equipment for liquids and the like, in which a rotor structure spreads the liquid in a thin film on the inner Wall of a surrounding jacket, there is always the possibility of the liquid film being diminished to such an extent by evaporation that the rotor structure can no longer work it properly, so that parts of the inner jacket Wall are not maintained wet.

This possibility is a particular problem in thin film apparatus employing rotor structures having rigid blades which must be provided with a sufiicient clearance at the jacket wall to anticipate the changes in structural relations that result from differential thermal influences during operation. The same problem is also encountered to some extent in apparatus having movable rotor blade elements, such as brushes or wipers, and the result is a troublesome local baking or coking of the material being processed at the unwetted jacket wall area.

Several special arrangements have previously been employed for avoiding this difficulty. One such arrangement has employed a conical heat exchanger in which the feed is at the larger diameter and the concentrate discharge outlet is at the smaller diameter, so that the inner wall area to be wetted decreases as evaporation decreases the quantity of material available for Wetting. Such an arrangement, however, is only useful for a certain evaporating ratio. If this ratio is changed then the rotor is either overloaded or the inner wall surface is not maintained properly wet.

Another possible arrangement is to pump the material to be processed in at the bottom of the heat exchanger for spreading over the inner wall by the rotor structure and discharge at the top. An arrangement of this sort has the disadvantage of requiring a higher than usual rate of throughput, so that increased hydrostatic pressure reduces the thin film advantages. In addition, it does not allow the residence time to be controlled; it results in much higher energy consumption; and, upon shutting down operation, it leaves a substantial quantity of material to drain back into the feed supply and degrade its quality.

The present invention makes it possible not only to increase residence time during the processing treatment, but to control the residence time as Well. This is done by directing the discharge flow inwardly with respect to the axis of the rotor structure so that it is opposed by centrifugal force exerted by the rotor structure to obtain the desired residence time increase.

The means by which this result is accomplished according to the present invention may be used for liquids of all kinds, such as solution, emulsions, Suspensions and molten solids, as well as for all fiowable solids such as 3,228,453 Patented Jan. 11, 1966 may result from drying or crystallization processes. Good performance is achieved at the operating conditions required in all sorts of thin film apparatus; i.e., evaporators, fractionators, dryers, reactors and the like. It is only necessary that the rotor r.p.m. be maintained sufliciently high to exert an appropriate centrifugal force opposition.

The effect of the centrifugal force opposition is to dam up the dicharge flow so that it assumes the form of a rotational paraboloid under the influence of the rotor. The height to which this damming effect extends is dependent on the rotor speed; on the extent to which the discharge flow is directed inwardly; and on the viscosity of the material being processed. By changing the extent of the inward discharge flow direction, the degree of damming and the consequent mean residence time may be selected to suit the condition at hand. It is preferable to limit the extent of inward direction so that a sufliciently large discharge outlet remains to avoid hinderance of the discharge flow by the rotor structure and any consequent necessity for dealing with the discharge flow speciaL ly at the outlet.

The means of the present invention may, in particular, offer special advantages in thin film apparatus incorporating multiple processing zones. Thus, in apparatus having a first zone provided for bringing in a material up to reaction temperature; then a second zone in which another material is added to achieve a chemical reaction; and, finally, a third zone for cooling the reaction product; the present invention may be employed, for example, to control eifectively the residence time in the reaction zone.

Tests have shown that surprisingly good results are achieved in evaporating liquids of low and medium viscosities; the heat transfer coeflicients, capacity, and evaporation ratio all being remarkably improved in a thin film evaporator having a rigid blade rotor structure, without in any way lessening the quality of the product.

Such tests have also shown that the rotor speed, in order to provide satisfactory damming opposition, should be at least about 20 feet per second at its periphery and preferably more than about 30 feet per second. Also,

the discharge directing means and the adjacent portion of the rotor structure must be related specially so that a good performance is not only afforded as the processing operation is started, but is also maintained despite the dimensional changes that result during operation by reason of the differential thermal influences to Which the jacketed processing chamber and rotor structure are, respectively subjected.

It is preferable to have the apparatus arranged so that the rotor axis extends vertically, because the discharge flow is more easily handled when this is so. However, the invention may still be employed advantageously in apparatus that is disposed so as to tilt the rotor axis, or even to position it horizontally, where special operating or installation conditions require this to be done.

The invention is described in further detail below in relation to the accompanying drawings, in which:

FIG. 1 is a side elevation, partly broken away and sectioned, illustrating thin film apparatus of the type in which the present invention is applicable;

FIG. 2 is a vertical sectional detail of a modified rotor and chamber arrangement;

FIG. 3 is a further sectional detail taken substantially at the line 33 in FIG. 2;

FIG. 4 is a central section of thin film apparatus having the rotor positioned horizontally to illustrate the application of the present invention in such an arrangement;

FIG. 5 is a fragmentary central section of further modified thin film apparatus in which the operating effect of the present invention is additionally illustrated;

FIG. 6 is a fragmentary sectional detail showing a preferred arrangement embodying the present invention;

FIG. 7 is an additional fragmentary section showing a modified embodiment of the preferred FIG. 6 arrangement; and

FIG. 8- is another fragmentary section showing a second modified embodiment of the preferred FIG. 6 arrangement.

In FIG. 1, the reference numeral 1 indicates a cylindrical processing chamber surrounded by a jacket 2. A top cover 3 incorporates a bearing 4, and a conical bottom section 5 is similarly arranged to support a rotor shaft 6 at a bushing 7; the latter being made adjustable by a bolt 8. The rotor shaft 6 is fitted with rigid blades 9 whose peripheral edges lie near the inner surface of the chamber 1 and whose length corresponds at least to the chamber jacketing 2; and the shaft 6 is driven by a motor (-not shown) through V-belts 10 running to a pulley 11 thereon.

The chamber jacketing 2 has a steam inlet 12 and a condensate out-let 13 connected therewith. The material to be processed is fed to the chamber 1 through a feed line 14, and the bottom product is discharged through an outlet 19 in the conical bottom section 5, while the over head vaporized product is taken off at 15 by suitable condenser and vacuum source means (not shown).

The conical bottom section 5 has an annular flange portion 16 by which it is suited for assembly in the ap paratus, and which forms an upwardly facing circumferential shoulder 17 at the lower end of the chamber 1 that extends inwardly toward the axis of the rotor shaft 6 in the extent indicated by the reference numeral 18. The material being processed, upon introduction through the feed line 14, is spread by the rotor blades 9 to thin film form over the inner surface of the chamber 1 as it flows downwardly therein under the influence of gravity and is subjected to heat transfer by means of the jacketing 2. The shoulder 17 causes the discharge flow of material from the chamber 1 to change direction inwardly of the apparatus and in opposition to the influence of the rotor blades 9 before entering the conical bottom section 5 for ultimate discharge at 19. It is preferable to maintain the clearance of the rot-or blades 9 at the shoulder 17 smaller than the clearance within the chamber 1, and this may be done by adjustment through the previously mentioned bolt 8.

FIGS. 2 and 3 illustrate a modified rotor structure incorporating blades 21 carried by a shaft 22 with a processing chamber having stepped portions 23a, 23b and 230 that successively decrease in diameter so as to form shoulders at 24 and 25 over which material being processed must pass as it flows downwardly in the apparatus. The shoulders 24 and 25 may differ in width to provide a residence time as desired in the respective chamber portion or section (23a or 23b) thereabove, and the successive chamber sections may be diiferentially heated or cooled so as to allow progressive processing not only at different residence times but at different temperatures as well. Additionally, it is posible to arrange the rotor structure so that its temperature may be controlled to induce condensation of liberated vapors thereon. Thus, there are broad possibilities for application of the present invention in carrying out chemical reactions, fractionation and other processes in thin film apparatus.

FIG. 4 shows a further apparatus variation in which the rotor st uct re is arranged on a horizontal axis and the processing chamber 26 is of conical form. The horizontal rotor shaft 27 carries blades 28 shaped to present their outer edges at a film forming clearance within the conical processing chamber 26. At its smaller end, the conical chamber 28 has a cylindrical portion 29 connected therewith that is fitted with a cover 30, while the larger end of chamber 28 is formed with a flange 31 in which an annular ring member 32 is seated and retained in place by an overlying flange of a cylindrical portion 33 provided in a cover structure 34 that is fitted with a drain outlet 36 and a vapor connection at 37. If desired, an additional vapor connection might be arranged at 37a so that processing might be either concurrent or contra-current. A feed connection 33 is provided at a higher level than the outlet 36, and the annular ring member 32 forms a barrier having its lowest point lower than the junction of the conical processing chamber 26 with its cylindrical extension 29 at 39. The feed through the inlet 38 enters the cylindrical extension 29 for delivery to the processing space within the conical chamber 26 under the influence of the rot-or blades 28; the residence time of the fed material within the chamber 26 being determined by the annular ring member 32 over which the material must flow to reach the drain outlet 36. Suitable jacketing (not shown) is provided about the processing chamber 26 to obtain the temperature conditions needed for processing.

FIG. 5 shows still another apparatus arrangement in which a vertical processing chamber 40 of cylindrical form, that should be understood to be surrounded by jacketing (not shown), is formed with a bottom end flange 41 for fitting with a bottom conical cover 42 at a flange portion 43 thereof; the bottom cover 42 terminating in a discharge outlet at 44. Between the flanges 41 and 43 a first ring member 45 is seated to carry supports 46 for a lower rotor shaft bearing 47, and a second ring member 48 is retained to form an inwardly extending shoulder at the lower end of the processing chamber 40. The rotor shaft 49 is formed with sup-ports as at 50 for hinging rotor blades 52 thereon as indicated at 51. During operation the hinged blades 52 are centrifugally positioned either to drag over the inner surf-ace of the chamber 40 to assume a radial position at a film forming clearance therewith.

As the material being processed flows downwardly through the chamber 40 under the influence of the rotor blades 52, it is forced to change direction upon reaching the shoulder formed by the annular ring member 48 so as to flow inwardly toward the rotor axis. When this occurs, the opposing centrifugal force exerted by the action of the rotor blades 52 acts to dam up the material flow in the form of a rotational paraboloid above the annular ring member 48 as indicated at 53. The slope of the paraboloid surface at 53 is determined by the r0- tating speed of the rotor blades 52, and this slope influences the height above the annular ring member 48 to which the damming eflect extends. The Width of the ring member 48 also influences this height, a greater width resulting in a greater height; and the height is additionally influenced by the friction forces and viscosity of the material being processed.

This discharge flow after passing over the inner edge of the ring member 48 proceeds through the opening 55 about the lower rotor blade support 50 and into the bottom cover structure 42 for pumping out at the outlet 44. To have steady operating conditions, the opening 55 should be big enough to assure a free discharge flow from the processing chamber.

The material at the rotational paraboloid 53 is subject to internal circulations that assure good mixing. Such mixing increases with lower material viscosity and at higher rotor blade speeds. When higher material viscosities are dealt with a wave tends to form in front of the rotor blades, and this front wave formation can be reduced by not-ching the rotor blades as at 54, or by bending the rotor blades 52 forwardly in the region of the paraboloid 53. Forward bending of the rotor blades 52 in this manner also increases internal mixing.

FIGS. 6, 7 and 8 illustrate arrangements by which the rotor structure may be suited advantageously to maintain an operating relation for damming the discharge flow effectively despite dimensional displacement occurring during operation by reason of differential thermal infiuences on the processing chamber and rotor structure.

In FIG. 6, the annular ring member 56 is shaped specially so that its upper surface facing the discharge flow has an elevated inner edge at 57 and slopes downwardly to a lower outer edge 58 at the inner wall of the processing chamber. The slope angle A is preferably in the orden of 120 to 135 and the adjacent portion of the rotor blades 60 is formed with a complementary shape as shown in FIG. 6. As a result, the specially shaped annular ring member 56 acts to puddle the discharge flow at substantial depth just prior to discharge, and the complementary shape of the rotor blades 60 act in turn to sweep this puddied discharge flow so as to maintain an effective centrifugal opposition thereto despite dimensional displacement during operation in an extent as great as is indicated at a in FIG. 6. At least one drain channel 61 is formed to extend through the ring member 56 from its upper face and adjacent its lower edge 58 so that all puddled discharge flow will be released whenever operation of the apparatus is stopped.

In the different arrangement shown by FIG. 7, the rotor blades 62 are fitted with slideways 63 for carrying relatively small plate members 64 formed of some suitable material such as graphite or Teflon, and acting under the influence of gravity to maintain an effective operating relation with the discharge directing shoulder 65 by shifting in the slideways 63 to compensate for dimensional displacement as it occurs.

FIG. 8 shows a further differing arrangement in which the upper face 66 of the annular ring member 67 slopes downwardly toward the rotor axis at a slope angle B that is less than 90, and that has been found to be effective when reduced as low as 20. Such downward sloping of the ring member 67 assures complete draining of the discharge flow without requiring special provision therefor, such as the drain channel 61 in the FIG. 6 ring member. The related rotor structure incorporates blades 68 on which guides 69 are arranged to carry plates 70 that have head pieces 71 thereon to abut the guides 69 for determining a lowest position of the plates 70. The plates 70 are carried to shift at an inclination with respect to the rotor axis so that a centrifugal force component as well as gravity acts to maintain their operating relation at the ring face 66. Also, the active edge 72 of these plates 70 may be shaped, as by beveling or the like, so that hydraulic influences are employed to avoid any undesirable degree of mechanical friction at the ring face 66.

The representative structures described above incorporate the usual star shaped arrangement of radially extending rotor blades, either rigid or hinged. However, other forms of rotor blades may be used as well. For example, if conditions are such as to make maintenance of a freely flowing discharge, the rotor blades may be bent backwardly in the discharge zone, or an opening may be provided between the inner edges of the blades and the rotor axis. Also, the rotor blades might be formed forwardly or backwardly so as to assume a spiral shape from top to bottom.

With an arrangement such as is shown in FIG. 6, numerous tests have been performed to compare evaporating ratios with and without the annular ring member 56. These tests were performed in a thin film evaporator having a heating surface of 1.4 sq. ft. at an internal diameter of 82 mm. The ring member 56 used had an internal diameter of 72 mm. The rotor structure was equipped with rigid blades, and the blade clearance 6 at the inner wall of the processing chamber was 0.8 mm.

Comparative tests were made for water and for monoethylene glycol, with results as tabulated below:

Test 1 Product Water. Operating pressure mm. Hg abs. Heating steam 107-109 p.s.i. Heating steam temperature l72 C. Vapor temperature 54 C. Temperature difference 116-118 C. Rpm. of rotor 1950 r.p.m.

Feed Bottom product,

. Overhead Ring product,

kgJh.

Evaporatmember ing ratio KgJh. C.

With Without.

With

Without.

With With0ut Test 11 Product MEG Monoethyleneglycol. Operating pressure 5.5 mm. Hg abs.

Heating steam 50-53 p.s.i.

Heating steam temperature 146148 C.

Vapor temperature 767'7 C.

Temperature difference 71 plus or minus 1 C. Rpm. of rotor 1950 r.p.rn.

Feed Bottom product,

Overhead product, kg./h.

Ring

Evaporatmember ing ratio KgJh. C.

With Without With Without;

With Without With Without.--

The present invention has been described in detail above for purposes of illustration only and is not intended to be limited by this description or otherwise except as defined in the appended claim.

I claim:

1. In thin film apparatus of the type incorporting a rotor structure having blade elements by which fluent material fed to the apparatus is spread in thin layer form over a surrounding stationary surface within the apparatus while being caused by gravity to flow downstream along said surface for processing treatment, the improvement which comprises annular damming means fixed at the downstream end of said surface and extending inwardly thereat for causing an inward overflowing of said fluent material from said surface that is opposed by centrifugal force exerted by the blade elements of said rotor structure to impose on the downstream flow of said fluent material along said surface the form of a rotational paraboloid reaching upstream from said damming means and thereby increase the residence time of said fluent material on said surface, all portions of said apparatus and of said rotor structure downstream of said damming means being free of any flow forcing blade elements and being formed for accommodating the inward overflowing of said fluent material for continuing downstream flow at a sufficient rate to avoid any retrogressive influence from said continuing downstream flow on the inward overflowing caused by said damming means.

2. In thin film apparatus of the type incorporating a rotor structure having blade elements by which fluent material fed to the apparatus is spreadin thin layer form over the surounding inner surface of a stationary cylindrical chamber Within said apparatus while being caused by gravity to flow downstream through said chamber for processing treatment therein and ultimate discharge therefrom, the improvement which comprises annular damming means fixed at the downstream end of said cylindrical chamber and extending inwardly thereat from said inner chamber surface for causing an inwardly directed discharge overflowing from said chamber that is opposed by centrifugal force exerted by the blade elements of said rotor structure to impose on the downstream flow of said fluent material through said chamber the form of a rotational paraboloid reaching upstream from said damming means and thereby increase the residence time of said fluent material on said inner chamber surface, all portions of said apparatus and of said rotor structure downstream of said damming means being free of any flow forcing blade elements and being formed for accommodating the discharge overflowing from said chamber at a continuing downstream flow rate suflicient to avoid any retrogressive influence from said continuing downstream flow on the inwardly directed discharge overflowing caused by said damming means.

3. In thin film apparatus, the improvement defined in claim 2 and further characterized in that said annular damming means is formed by a ring member having a surface facing said downstream fluent material flow through said chamber with an upstream inclination toward the axis of said rotor structure in opposition to said downstream flow, and in that the adjacent portions of said rotor structure blade elements have a complementary shape.

4. In thin film apparatus, the structure defined in claim 3 and further characterized in that said ring member is formed with at least one drain channel extending therethrough from an opening in said facing surface adjacent the inner surface of said cylindrical chamber.

References Cited by the Examiner UNITED STATES PATENTS 1,308,819 7/1919 Taylor 1596 1,420,648 6/1922 Mabee 1596 1,420,649 6/1-922 Mabee 1596 1,435,295 11/1922 Hay 1596 X 1,466,579 8/1923 Collver 1596 2,169,601 8/1939 Cornelius et al 1596 X 2,551,630 5/1951 Bierwirth 1596 X 2,580,646 1/ 1952 Belden.

2,623,580 12/1952 Arnaud 1596 2,774,415 12/ 1956 Belcher 1596 2,866,499 12/1958 Haley -a 1596 2,884,050 4/1959 Brownell 1596 3,067,812 12/1962 Latinen et al. 1596 3,110,646 11/1963 Mayhew et al 1596 3,129,132 4/1964 Gudheim 1596 X FOREIGN PATENTS 25,634 1897 Great Britain.

NORMAN YUDKOFF, Primary Examiner. 

1. IN THIN FILM APPARATUS OF THE TYPE INCORPORTING A ROTOR STRUCTURE HAVING BLADE ELEMENTS BY WHICH FLUENT MATERIAL FED TO THE APPARATUS IS SPREAD IN THIN LAYER FORM OVER A SURROUNDING STATIONARY SURFACE WITHIN THE APPARATUS WHILE BEING CAUSED BY GRAVITY TO FLOW DOWNSTREAM ALONG SAID SURFACE FOR PROCESSING TREATMENT, THE IMPROVEMENT WHICH COMPRISES ANNULAR DAMMING MEANS FIXED AT THE DOWNSTREAM END OF SAID SURFACE AND EXTENDING INWARDLY THEREAT FOR CAUSING AN INWARD OVERFLOWING OF SAID FLUENT MATERIAL FROM SAID SURFACE THAT IS OPPOSED BY CENTRIFUGAL FORCE EXERTED BY THE BLADE ELEMENTS OF SAID ROTOR STRUCTURE TO IMPOSE ON THE DOWNSTREAM FLOW OF SAID FLUENT MATERIAL ALONG SAID SURFACE THE FORM OF A ROTATIONAL PARABOLOID REACHING UPSTREAM FROM SAID DAMMING MEANS AND THEREBY INCREASE THE RESIDENCE TIME OF SAID FLUENT MATERIAL ON SAID SURFACE, ALL PORTIONS OF SAID APPARATUS AND OF SAID ROTOR STRUCTURE DOWNSTREAM OF SAID DAMMING MEANS BEING FREE OF ANY FLOW FORCING BLADE ELEMENTS AND BEING FORMED FOR ACCOMMODATING THE INWARD OVERFLOWING OF SAID FLUENT MATERIAL FOR CONTINUING DOWNSTREAM FLOW AT A SUFFICIENT RATE TO AVOID ANY RETROGRESSIVE INFLUENCE FROM SAID CONTINUING DOWNSTREAM FLOW ON THE INWARD OVERFLOWING CAUSED BY SAID DAMMING MEANS. 